The present invention relates to the manufacture of golf balls and more particularly to the formation of molds used in producing the balls.
Golf ball molds are used to manufacture the dimpled covers for both two-piece golf balls, i.e., the type having only a solid core and the outer cover, and three-piece balls, i.e., the type having a similar core but with elastic windings around it. Normally, two oppositely facing molds (an upper and a lower) are used to make the dimpled cover with each mold having a hemispherical, dimpled mold cavity that is generally the size of one-half the "finished" ball. When the two molds or mold "halves" are mated, they form a generally spherical interior with a dimpled contour that is basically a negative image of the golf ball cover that will be produced inside of it.
One method of making golf balls is to utilize oppositely facing hemispherical, dimpled shells in an injection molding process. Instead of the mold halves being unitarily formed with hemispherical, dimpled cavities, the shells are separately formed and are later fixed inside the halves. With this injection molding process, the mold halves (and attached shells) are initially moved apart to accept the center core of a golf ball. Afterwards, the mold halves are pushed together to form a spherical housing for the center core, and two pins in the bottom half extend upwardly and lift the ball's core to the center of the mold cavity. Then, the molten material for the ball's outer shell is injected into the cavity around the raised core.
Recent studies conducted by the manufacturers of golf balls have indicated a definite need for accuracy and consistency on the physical measurements of the dimples on golf balls as well as a need to produce complicated and exotic dimple shapes and patterns. These conclusions are the results of performance and wind tunnel testing.
Since the golf ball receives its dimple impressions from the golf ball mold, the integrity of the dimples will be dependent upon the accuracy of the molds used. Accordingly, it is extremely important that an improved process be developed for accurately making consistently-shaped, well-formed golf ball molds. Further, it would be ideal if the process were inexpensive.
In recent history, golf ball molds have been made by hobbing, as described in U.S. Pat. No. 3,831,423, or by die forming, as described in U.S. Pat. No. 3,543,380. The advantage of hobbing is that a metal is forced to conform to a very accurately machined master or hob. Thus, the dimples or indentations on the mold are an accurate replica of the hob. The disadvantage of hobbing is that the metal used to make the mold must be very soft in order to "flow" enough to adequately conform to the hob. The resulting mold from the hobbing process has a short useful life because it is subjected to considerable loads in the manufacture of golf balls and, being very soft, is susceptible to deformation and damage.
The die-forming process described in U.S. Pat. No. 3,543,380 has the advantage of using harder material, including stainless steel, to construct the mold. However, the dimples formed are less accurate than with a hobbing process and are subject to variation from mold to mold.
Accordingly, it is the primary object of the present invention to provide an improved method and apparatus for making extremely accurate golf ball molds.
It is another primary object to provide an improved method and apparatus for making accurately formed, dimpled hemispherical shells for use in golf ball molds.
It is another general object to provide an improved method and apparatus for making accurately machined mold shells that are durable and substantially duplicative of one another.
It is a specific object to provide an improved method of exactly duplicating a master die or hob while still allowing the use of durable construction materials for the mold.
It is a more specific object to provide a method and apparatus of making mold shells in which the shell product is substantially an exact negative of the dimpled master and an exact duplicate of every other shell produced on that master, thus giving the advantages of the hobbing process described in U.S. Pat. No. 3,831,423. However, in this improved method, harder materials can be used than previously found in hobbing, thus giving the "durability" advantages of molds made with the die-forming process described in U.S. Pat. No. 3,543,380.
It is another object to provide method and apparatus, commensurate with the above-listed objects, that are easy to operate, require little operating training and are therefore economical to use.
The above and other objects and advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.